The present invention relates to writing pens and more particularly to writing pens utilizing relatively low viscosity liquid inks particularly, but not necessarily, for stylus or ballpoint pens. Writing pens of this general type, utilizing low viscosity liquid inks, are preferred for many applications over older style ballpoint pens, for example, which utilize a high viscosity ink. The low viscosity inks provide for a much smoother writing action and a more intense written line than the high viscosity inks. When using low viscosity inks, however, special provisions must be made to prevent leakage of the ink and/or to properly control the flow of ink during writing. A generally preferred form of inexpensive pens for this purpose utilizes a so-called vacuum reservoir for the liquid ink, in conjunction with a capillary collector that enables ink to be fed to the writing tip and also enables the reservoir to xe2x80x9cbreathexe2x80x9d in response to the consumption of ink and/or to changes in temperature and pressure. The general principles of such pens are well known as set forth in, for example, the Wittnebert U.S. Pat. No. 3,951,555.
The present invention provides a writing pen of the general type described above, which can be economically produced and which has superior writing characteristics. More particularly, the invention is directed to a type of writing pen, usually but not necessarily non-refillable, in which an ink reservoir is formed by the main body of the pen. The body is preferably formed of a molded plastic material, closed at one end and open at the other. The open end of the pen body is closed by a collector cartridge, provided with a plurality of closely spaced circular fins or lamellae and capillary passages. A writing element, preferably but not necessarily a ballpoint tip, is mounted at the lower end of the collector cartridge and is provided with a capillary rod which extends into a central through passage in the collector cartridge and thus communicates with the ink supply contained in the pen body reservoir, above the collector cartridge.
As ink is consumed from the reservoir, it is replaced by air drawn in through the collector cartridge. Both the ink in the reservoir and the air above the ink are influenced by changes in temperature. In a pen construction in which the primary pen body forms the ink reservoir directly, as distinguished from constructions in which there is a separate ink-holding cartridge contained within the pen body, heat from the hand of the user tends to be conducted into the pen body, heating both the ink and the air contained in the reservoir. As will be appreciated, this can have a variable influence on the manner in which the pen operates. Experience shows that this variability becomes more acute as ink is consumed, because the air volume contained in the reservoir is more responsive to changes in temperature than the ink itself, and that variability becomes more acute as the relative amounts of air in the reservoir increase in the course of ink consumption.
Pursuant to the present invention, the body of the pen is designed with outwardly extending elements, preferably formed by deep flutes or grooves in the upper portion of the pen body. This includes the region of the internal reservoir and preferably also that portion of the pen body above the reservoir, in cases where the reservoir occupies only a portion of the pen body. The outwardly extending elements, e.g., deep flutes or grooves, perform two functions: The first is to form an interrupted outer surface of the pen body, to restrict the area of contact between the pen body and the hand of the user, particularly in the region of the ink reservoir. This serves to limit and restrict the transfer of heat from the user""s hand into the ink and/or air contained within the reservoir. Secondly, the outwardly extending flutes, grooves or other elements provide significantly greater exposed surface area for radiating and conducting heat away from the pen body so that heat that is unavoidably added by reason of the writer""s grip can be more efficiently dissipated. In an inexpensive pen of the type contemplated, where the pen body itself forms the reservoir for the liquid ink, there is a direct path for the conduction of heat from the outside of the pen body to the interior of the reservoir. Particularly where a substantial portion of the ink has been consumed, and the air volume is relatively large, heat input from the user""s hand can result in significant expansion of the air volume, tending to force the low viscosity ink out of the main reservoir and into the collector cartridge. While the intended purpose of the collector cartridge is to temporarily receive ink displaced by such expansion, excessive amounts of such expansion can be deleterious to the performance of the pen and are minimized by the pen construction of the invention.
It is contemplated that the new pen will be furnished with inks of various colors, for artists, etc. To this end the pen is provided with a nib which is color coded to indicate the color of the ink contained within the pen. Additionally, a novel cap is provided, which fully exposes the colored nib and enables the artist to quickly ascertain the pen""s color without either removing the cap or rotating the pen to a position in which the nib may be viewed through a special window. The pen body and cap may be made out of a material of common color (e.g., black) to achieve economies of manufacture, while at the same time enabling the user to ascertain ink color by simply viewing the cap.
A preferred form of the invention also includes an improved nib-collector cartridge designed to facilitate precision molding procedures. To this end, the cartridge includes an axially extending, generally tubular gate element at its upper end, formed with an opening at one side to accommodate ink flow and mold ejection.
For a more complete understanding of the above and other features and advantages of the invention, reference should be made to the following detailed description of a preferred embodiment, and to the accompanying drawings.